Instructions for Using the On-Site Electrolytic Polishing and Etching Unit
Insert the cathode body and sponge into the cathode sleeve, then connect one end of the wire to the cathode body and the other end to the negative terminal of the power supply. Before use, ensure the sponge is saturated with sufficient chemical reagent, and that the cathode body and sponge are in full contact. Insert the anode body and magnet into the anode sleeve, securing the anode body to the magnet with thin double-sided tape. Connect one end of the wire to the anode body and the other end to the positive terminal of the power supply. For workpieces made of ferromagnetic materials, there is no need to use thick double-sided tape; the anode assembly can be secured near the test point using only the magnet. For workpieces made of non-ferromagnetic materials, thick double-sided tape must be attached to the bottom of the anode sleeve to secure the anode assembly near the test point.
During use, ensure the sponge inside the cathode assembly absorbs sufficient chemical reagent, and bring the sponge saturated with the reagent into full contact with the metallographic inspection point on the large workpiece. Secure the anode assembly near the metallographic inspection point. Connect the power supply; under the action of a certain current, the metallographic inspection point on the large workpiece will achieve the effects of electrolytic polishing and etching.
Effects of Electrolytic Polishing and Etching
Common engineering materials such as 20MnNiMo low-alloy steel, 06Cr119Ni10 stainless steel, and 00Cr30N60Fe10 nickel-based high-temperature alloy were selected for on-site metallographic electrolytic polishing and etching tests. Prior to on-site electrolytic polishing, the surfaces to be inspected were first rough-ground using 120-grit and 320-grit sandpaper to remove surface scale and coarse scratches.
For the 20MnNiMo low-alloy steel, an electrolytic polishing solution consisting of 46% phosphoric acid + 15% sulfuric acid + 2% oxalic acid (saturated aqueous solution) + 18% water (all percentages are by volume) was used. The electrolytic polishing current density was 1.0–2.5 A/cm², and the duration was 30–120 seconds; Then, wipe the surface with a 4% nitric acid-alcohol solution to perform chemical etching. The resulting microstructure morphology is shown in Figure 5.
For 06Cr19Ni10 stainless steel, electrolytic polishing was performed using an electrolytic polishing solution consisting of 500 g of phosphoric acid, 150 mL of sulfuric acid, and 1000 mL of water, with a current density of 1.0–2.5 A/cm² and a duration of 30–80 s. Then, electrolytic etching was performed using a 10% oxalic acid solution, with a current density of 0.1–0.3 A/cm² and a duration of 5–30 s. The resulting microstructure is shown in Figure 6.
For the 00Cr130N60Fe10 nickel-based high-temperature alloy: Electrolytic polishing was performed using an electrolytic polishing solution consisting of 120 mL of magnetic acid, 30 mL of water, 30 mL of sulfuric acid, 5 mL of acetic acid, and 50 g of oil, with a current density of 1.5–2.5 A/cm² and a duration of 20–30 s. Subsequently, electrolytic etching was performed using the same electrolytic polishing solution, at a current density of 0.2–0.5 A/cm² and a duration of 2–8 s. The resulting microstructural morphology is shown in Figure 7. As can be seen, the on-site electrolytic polishing and etching device designed and developed demonstrates good performance in both electrolytic polishing and etching, clearly revealing the microstructures of different materials, and is suitable for on-site metallographic inspection of large workpieces.
